Impact of Ambient Gases on the Plasma Radiation and its Expansion in Laser-Copper Interaction

In this paper, the impacts of air, argon, helium and neon ambient gases under different gas pressures on radiations, emphasizing in the signal to radiation background and the expansion of laser induced plasma from laser metal interaction have been experimentally studied using spectroscopy, probe beam absorption, and scattering methods. The results show that the plasma radiations and its expansion behavior depend strongly on the ambient gas presure. The highest intensity of the copper spectral lines occurred in argon, neon, air, and helium, respectively. For all gases, by increasing the gas pressure from 5 to 100 mbar the plasma spectral radiation increases and then it saturates at the higher gas pressure. The continuum radiation also increases with the pressure and has the highest value for Ar, air, Ne and He gases, respectively. Plasma in He, Ne, air and Ar has the best singnal to backgrourd (S/B) ratio, respectively, and decreases with the pressure. The probe beam absorption and scattering results have also been compared with the Sedov-Taylor strong shock wave model. The maximum speed of the plasma plume expansion, occurred near the target surface under 750 mbar gas pressure, and was determined for helium to be about 25200 m/s, and through neon, air and argon gases, amounted to about 15625, 13900 and 11860 m/s, respectively, as they reduced significantly when they were far from the target surface and reached 2550, 1000, 700 and 690 m/s at 6 mm from the target for helium, neon, air and argon, respectively.